By Dave Solberg
Dear Dave,
I have a valve at the end of my sewer pipe to prevent “surprises.” Lately, when it starts to dump, before I open the black tank valve, I open the sewer pipe end valve and out comes brown (black tank) waste. Is my black tank valve leaking? If it is, what can I do to fix it? —Doug, 2021 Open Range 314RLS
Dear Doug,
The small valve at the end of your sewer pipe is most likely a 3/4” threaded outlet that has a small cap. This is the size of a garden hose and designed to allow you to take the cap off and verify the main black tank pipe is not full of sewage.
It has a bayonet connection similar to the standard cover on the dump valve that will allow you to connect the dump hose.
As you have found, this smaller cap is a better way to verify there is sewage. It can be loosened slightly and, if there is fluid, can be tightened without too much “junk” flowing out all over the place before you can get the dump hose attached.
Black water tank valve not closing all the way
Since you have some sewage or “brown water” coming out, it indicates your black water tank valve is not closing or seating all the way. This is a spade-type valve, usually a Valterra brand, and looks similar to this.
Some models have the handle accessible directly on the valve like this one. Others have the valve hidden underneath and a cable going to a remote handle. If you have a remote system, the first thing I would check is how tight the cable is. If you can get to the actual valve, make sure the “gate” or spade is closing all the way. These cables can stretch and need to be adjusted or tightened.
If the valve is not seating, it could be something lodged in the rubber seal and not allowing the spade to close all the way. Or it could be a bad seal. You will need to find a way to dump what is in the tank and flush it out—which is typically a messy job. Hopefully, the leak is minor and you can get a dump hose on it quickly without much of an issue.
Flush the black tank out
I would then try flushing the black tank out with either a garden hose down the toilet or connect a black water flush hose, if your rig has one. Leave the valve open and let water flow through the valve and occasionally close and open it to help dislodge anything that might be sticking to the spade or rubber gasket. You might try Thetford’s Tank Blaster once to see if it cleans it up. You can find it on Amazon here.
You might also try the Thetford Drain Valve Lubricant after flushing out the tank. You can find that product on Amazon here.
Most of the time the valve just has developed a bad seal and you can replace the seal or the entire valve. However, I have found it is much easier to just add a valve adapter to the end of the bayonet. You can get this twist-on adapter that attaches to the standard bayonet pegs and adds an easy open and close valve without all the mess. You can find it on Amazon here.
You might also enjoy this from Dave
My RV’s black tank valve used to trickle when taking cover off; now it gushes!
Dear Dave,
Whenever I dump the RV’s black water tank, usually a small amount comes out when I remove the cap. Because of this I carry a small bucket to catch the spillage. However, this last time when I removed the cap I was met with a flood of black water. Is there some way to clean the valve? I’m not even sure where the valve is, since the belly is covered. —Mike, 2020 Jayco Eagle 27.5
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RVDT2749
I recently changed our 3” black tank dump valve. Adding another valve to the end wasn’t an option on our camper as the assembly is already low to the ground. I did it at a campground so I could flush and clean the black tank first. I layed a bunch of paper towels down on top of a plastic trash bag to catch any liquids and easy way of disposal. It took a couple of attempts as the big O rings tend to flop and fall out, but I finally got everything lined up OK. Camper is a 2019 model.
Dave, I have a similar problem with a bit of leakage into my dump manifold. I use the cap with the small screw-on cap you describe in your article. When I prepare to dump, I put a bucket under the dump connection to catch any leakage from the small screw-on cap before I remove the manifold cap and attach my dump hose. I also wear disposable medical gloves anytime I handle dump hoses.